This invention relates to leech flaps for sails for sailboats.
The inventor is the inventor of U.S. Pat. No. 6,070,545, which is incorporated herein by this reference. In that patent, the inventor discloses and claims self-tacking leech flaps for sails for sailboats. Briefly, according to the invention of his issued patent, narrow flaps of sailcloth are added to the trailing edge or xe2x80x9cleechxe2x80x9d of a sail. The trailing edges of the flaps are sewn to the trailing edge of the sail, while the leading edges of the flaps are not attached to the sail. Instead, the leading edges of the flaps are joined to one another by light cords spaced at intervals along the length of the leech and extending through holes in the main membrane of the sail. These cords are of a length sufficient to allow the flap on the windward side of the sail to be pulled outwardly from the main membrane of the sail, forming a flow-impeding lip on the windward side of the sail. At the same time, the flap on the other side of the sail is pulled against the main membrane thereof, so that there is little increase in drag.
The flow-impeding lip thus provided on the windward side of the sail at the leech causes a low-pressure area to be formed behind the flap. This in turn pulls the flow on the leeward side of the sail closer to the leeward surface of the sail, which both increases lift and reduces drag.
The leech flaps provided according to the issued patent are self-tacking in that when the sailboat is tacked, that is, when the former leeward surface becomes the new windward surface, the flaps automatically reconfigure themselves, so that the flow-impeding lip is now provided on the new windward surface. Hence addition of the flaps according to the invention does not complicate ordinary sailing manuevers.
The present provisional application discloses several further improvements on the leech flaps of the parent patent. The principal improvement provided hereby is to the effect that the leech flaps are desirably serrated. That is, rather than being provided as continuous flaps joined to one another by strings provided at intervals, the flaps are configured as a series of opposed triangles (or comparably-shaped members) the apexes of which are joined by the strings; the bases of the triangles are secured to the trailing edge of the sail.
In a preferred embodiment, the triangles themselves are made up of relatively stiff xe2x80x9chigh modulusxe2x80x9d sailcloth, so that they hold their shape despite being secured by a single string at the apex of each. This material is too stiff to readily form a flexible hinge connecting the triangles to the main membrane of the sail. Accordingly, the triangles may be sewn to a ribbon of softer material, such as an ordinary taffeta ribbon, which in turn is sewn to the main membrane of the sail.
The height of the triangles is selected to be between 1 and 5% of the chord of the sail at their position along the leech; that is, the height of the triangles is reduced as the sail becomes more narrow towards the head.